Winter Dust vs Calcium Scaling, is there a difference?

Have you ever opened your pool after winter and you see these white flakes on the bottom of your pool and instantly think, “scale!” and then proceed to make a mental note to lower your calcium hardness levels the next year and end up with an even bigger problem! Not only that, but you also start to see some etching on your pool where the water has eaten away at your pool surfaces.

Winter Dust isn’t Calcium Scaling?

In a sense, yes, it’s a type of calcium scaling, but it’s really bad form to lump them together in one basket because treating/trying to prevent winter dust like calcium scaling will only increase the problem. The real way to prevent winter dust is to first understand what causes it. And no, it’s not caused by high calcium levels when you close the pool!

Believe it or not, winter dust is partially caused by low calcium levels in your pool when you close it for the winter! So by treating winter dust like it was caused by regular calcium scaling is simply just asking for trouble.

So what causes winter dust in pools?

We’ve covered this a couple of times in our articles that dealt with LSI or Langelier Saturation Index but we’ll go over it one more time, this time in a more condensed version. Basically your LSI is how corrosive (for low LSI) and how scale-formative (for high LSI) your water is. The most important thing to remember is that temperature plays a large part in determining your LSI values.

Even if your pool is fully protected during the winter, your LSI levels can swing from perfectly balanced, to corrosive, to scale-formative all in a couple of months without any other external factors except the temperature going down and up!

Winter Dust formation in a nutshell

If it isn’t due to high calcium levels then how exactly does winter dust form? To better understand it, let’s see what happens under the (winter) covers during the off-season.

  • You close your pool, everything is perfectly balanced. Life is good.
  • The temperature starts to drop, which in turn shifts your LSI down to the corrosive levels.
  • Due to the low LSI value, the water starts to eat away at your pool surfaces and increases the calcium levels of your pool water.
  • The calcium levels are high enough to bring your LSI back to the neutral level, the corrosion stops, life seems to be good.
  • The water starts to warm up, the temperature shifts your LSI back to where it was when the pool was closed, but this time, the water already has the added calcium!
  • The pool water’s LSI is now higher due to the added calcium and it will start to try to balance itself by precipitating the excess calcium out from the water, depositing calcium (winter dust) all over your pool, even in areas like pipes and the bottom of your pool where scale isn’t commonly found.
  • You open your pool and discover white splotches and winter dust everywhere. Life is not good.

Removing Winter Dust

Here’s where winter dust and calcium scale are alike. Removing winter dust from our pools is just like removing calcium scale. You can do a no-drain acid wash, or just manually removing them with some elbow grease and a good quality brush. You can even use a pool stone to clean out the surfaces once you’ve opened your pool. But this sounds like a lot of work right? I mean, why spend a lot of time and effort cleaning up winter dust when you can simply prevent it from occurring in the first place!

Preventing Winter Dust

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It takes a bit of science but we can actually prevent winter dust from occurring in the first place! All you need to prepare is to know what your average coldest temperature is during the winter, the temperature of your water when you close your pool and what the temperature will be when you plan to open your pool for the spring/summer.

Equipped with these three temperature values you can balance out your pool’s LSI level to stay within -0.30 and +0.30 for the entire off-season. The way we do this is to close our pools not at the perfect 0.0 LSI level but somewhere closer to the +0.2 to +0.3 level since we can anticipate your LSI levels to drop anywhere from 0.3 to 0.5 points, depending on how cold your location is. For example, you close your pool at +0.3 LSI (borderline for scale formative) and you’re located at a very cold location and your pool’s LSI levels drop by 0.5 points (or down to -0.2 LSI) this will still keep your water in the neutral range. Compare this is you didn’t account for the winter temperature and you balanced your LSI perfectly at 0.0, when it drops to the coldest point or -0.5 LSI, the winter dust formation that we described earlier will happen!

The easiest chemical level to adjust to pre-empt the drop in LSI during winter? Your calcium hardness levels!

What about calcium scale?

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Calcium Scale on the other hand is directly caused by high calcium hardness levels in your pool and this is something that we can actively combat by testing the pool water regularly and keeping it balanced. If we keep an eye out on our chemical levels (which is something that we should be doing on a regular basis anyway) then scale formation shouldn’t be a problem. The only places where we should be worried about scale are near our heaters and our salt water chlorinators due to the increase in temperature and pH around these areas. Much like winter dust, the best way to deal with scale is to prevent it from happening in the first place!

SEE ALSO: Recondition your spa just in time for winter


Removing Calcium Scale and Winter Dust

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Too late to the party and calcium scale has already set in? Good thing we have the solution for that sitting on our shelves. Introducing Scaletec Plus, the revolutionary pourable descaler designed specifically for swimming pools. Unlike traditional acid-based solutions, Scaletec Plus effectively removes calcium scale, iron stains, and scum without the need for scrubbing or pool draining. With its powerful Synertec formula, this high-performance descaler not only provides fast cleanup results within 2 to 4 weeks but also acts as a preventative measure against future stains.

Say goodbye to tedious maintenance tasks as Scaletec Plus effortlessly descales pool surfaces, tiles, and equipment, including filters, heaters, water auto-levelers, and solar units. Its non-acidic, non-staining, and low-phosphate composition ensures a safe and environmentally-friendly solution. Keep your pool pristine year-round with the convenience of Scaletec Plus, the ultimate calcium descaler trusted by pool owners everywhere.

SEE ALSO: Common Swimming Pool Mistakes Made During Winter


As with anything in our pool, proactive prevention of both winter dust and calcium scale is the best way to save time and money. All you need is a pen and paper, maybe 10 minutes to do the math and dosing/adjusting your pool chemical levels to the correct levels and that’s it. We can’t stress enough how proactive pool care is worlds better than leaving things to chance. Winter dust is not only a pain to clean, but remember, that dust has to come from somewhere, and that somewhere is your pool surfaces! While it won’t be apparent after one or two seasons, if this happens year after year after year, you’ll start to notice that your pool surfaces are already etched and “eaten” by the corrosive water and this can lead to hundreds, if not thousands of dollars in repair costs in the future.

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Bonus Section: Scale on Chlorinator Cells

If you're like us and you like to keep your chlorinators running over the winter to prevent your pool from turning green, it's now a great time to check them for scale so that your chlorinator will be in top form once spring/summer rolls in.

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The traditional way of cleaning a cell involves immersing the cell in some acid solution, we'd tackle that, but why when there's a better solution right? We have some salt cell cleaning solution that's so safe to use, it's actually marked as a non-dangerous good and can be shipped to your door! So if you discover scale on your chlorinator cell, don't forget to order some non-DG salt cell cleaner and follow the guide below to recondition your chlorinator for summer.

For a more in-depth guideo on cleaning a chlorinator cell, check out our chlorinator cell cleaning guide here.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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